Lawn mower type is mostly a tradeoff between power and convenience, and which matters more depends heavily on the size and terrain of the actual lawn being mowed.
Gas, corded electric, or battery
Gas mowers offer the most power and unlimited runtime (as long as fuel is available), making them well suited to larger lawns, thicker or taller grass, and uneven terrain. The tradeoffs are regular engine maintenance (oil changes, spark plugs, carburetor issues if fuel sits too long), more noise, and exhaust emissions.
Corded electric mowers are quieter, need no engine maintenance, and start instantly, but are limited by the cord's length and the need for a nearby outlet, making them impractical for larger lawns or anywhere far from a power source.
Battery-powered mowers combine cordless freedom with electric mowers' low maintenance and quiet operation, but battery runtime limits how much can be mowed on a single charge, and battery capacity (and the resulting mower cost) needs to be matched to the actual lawn size to avoid running out of charge partway through.
Power source affects long-term cost, not just the purchase price
Gas mowers have ongoing fuel and maintenance costs (oil, spark plugs, occasional tune-ups) that add up over years of use. Electric and battery mowers have lower ongoing maintenance costs, but battery mowers eventually need a battery replacement, which can be a significant cost on its own. Comparing total cost of ownership over several years, not just the upfront price, gives a more complete picture than comparing sticker prices alone.
Cutting width and deck size affect mowing time more than most specs
A wider cutting deck covers more ground per pass, directly reducing the number of passes and total time needed to mow a given lawn area — a meaningful factor for larger lawns where mowing time adds up. For smaller or more complex yards with a lot of obstacles (trees, garden beds, tight corners), a narrower deck can actually be more practical despite requiring more passes, since it maneuvers more easily around obstacles.
The one thing people forget
Check the mower's actual weight and how easy it is to push, especially for a push (non-self-propelled) mower on sloped or uneven ground — a mower that's fine on flat, level ground can be considerably more tiring to push on a lawn with any real slope, and self-propelled models are worth the extra cost for anyone dealing with hills or a larger total area to cover.